A huge outage at Verizon is causing iPhones and Android devices to enter SOS mode, which prevents users from making mobile calls unless they utilize WiFi calling.

Verizon is adding satellite texting as soon as this fall, but not for all devices Phones enter SOS mode when not connected to their carrier network, either because they are in an area with poor coverage or because of a technical problem.

On Monday, Verizon suffered a massive outage that affected customers across the country. While it’s not clear exactly how many customers were without service, Verizon has more than 114 million customers in the U.